Error: Connect IQ SDK Manager doesn't continue after successful GAuth Embedded login

I downloaded the latest SDK Manager from developer.garmin.com/connect-iq/sdk/

Whether I am logged in or not to sso.garmin.com through one of Garmin's web applications:

At startup the SDK Manager fails to verify that I'm logged in to sso.garmin.com, and instead shows a Login button - Please fix this!

Clicking the Login button, a window with GAuth Embedded login page appears. This page fails to verify that I'm logged in to sso.garmin.com - Please fix this!

Entering valid username and password the GAuth Embedded login window doesn't close but shows an eternal spinning wheel, and SDK Manager doesn't continue startup - Please fix this!

Please advise on manual SDK files download:

Please advise how to download the required device files manually, i.e. the files in folder %userprofile%\AppData\Roaming\Garmin\ConnectIQ\Devices\fr965\ in my case. Where do I get the zip? I really need these device files, because the PacePro feature doesn't work on my FR 965 so I have to implement my own.

Ps. Right clicking the GAuth Embedded login window reveals the url that is used. Pasting this in the address bar of Chrome browser, gives a response with Service Ticket:
Either immediately if I've logged in through the GAuth Embedded login window of SDK Manager or through one of Garmin's web applications, or
after applying a valid username and password in the browser.